phd thesis department of hydraulic and environmental

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PhD Thesis Department of Hydraulic and Environmental Engineering

Riprap Design for Rockfill Dams

Priska Helene Hiller

Supervisors: Professor Leif Lia and Professor Jochen Aberle

Background

Rehabilitation of Svartevatn dam: placement of riprap stones on the downstram slope. Photo: NTNU Drawing of placed riprap

Downstream slopes of Norwegian rockfill dams are strengthened with a placed riprap against accidental overtopping or considerable leakage through the dam. Stones are placed in an interlocking pattern with their longest axis inclined towards the dam axis as shown in the figures. The current guidelines are based on the knowledge about dumped riprap despite the stones have to be placed in an interlocking pattern. Hence, there is need for more understanding of the additional strength gained by placed riprap.

Objectives of the study• Literature study of riprap design and practical solutions for steep slopes

• Identification of the hydrodynamic forces due to the flow over steep slopes and flow through the riprap

• Execution and analysis of laboratory tests and large-scale field tests

• Identification of the relevant parameters of the riprap material as well as the effect of placement patterns

This study is financed by Energy Norway and the Research Council of Norway. The support of the collaborating companies in the project “PlaF” is kindly acknowledged.

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BackgroundNorwegian hydropower plants are operated with an increasing number of start-stop operations, and variation of produced power. In addition, large hydropower pumped storage projects may be constructed in the near future.

To enable more flexible operation of the power plant, surge tanks may be constructed. The surge tank enables more rapid changes of the produced power, and reduces the pressure forces occuring during such maneuvers. The surge tank is also beneficial for regulation stability in large hydropower plants.

This PhD project seeks to investigate the optimum design of surge tanks, mainly focusing on the air cushion surge tank


Surge Tank Design for Hydropower Plants

Kaspar Vereide

Supervisors: Leif Lia and Torbjørn Nielsen

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Method for Reduced Uncertainty in Stage-

Discharge Curves

Øyvind Pedersen

Supervisors: Nils Rüther and Jochen Aberle

Background

The above figure shows an example of CFD-modelling similar to the methodology

studied in this PhD.

Getting reliable stage-discharge data under extreme flood conditions are essential for good predictions of future flood events. At the same time the discharge data used for prediction often have a high level of uncertainty. Getting more reliable flood predictions is potentially worth millions in saved costs for construction of dams and infrastructure, as well as in preventing damaging floods. The thesis aims to develop methodology for reducing uncertainty in stage-discharge curves using a hybrid-modelling approach. Hybrid-modelling involves combining a physical lab-model with a numerical CFD-model. The PhD-program is part of the Flom-Q project, which goal is to create a better flood-prediction framework for Norway.

The curve above shows a stage-discharge curve used for calculating discharge from a measured water level at a gauging station. Measurements of the stage-discharge relations typically is done for a range of discharges from low flow to flood conditions. However, at larger floods measuring discharges directly can be both difficult and dangerous, and by definition these floods are also rarely occurring events. Because of this, discharge data for extreme floods often stem from stage-discharge curves extrapolated well beyond the measured range. The goal of the PhD is to develop a method to obtain better data for the extrapolation.

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Water Consumption from Hydropower Production

By Tor Haakon Bakken

Supervisors: Ånund Killingtveit & Knut Alfredsen

BackgroundClimate change and the needed reductions in the use of fossil fuels call for the development of renewable energy sources. Today hydropower is the dominant renewable technology in the electricity system and in some regions extensive development of hydropower is expected in the coming years. Storage of water is often needed to overcome the hydrological variability, to the cost of evaporative losses from the reservoir surfaces. As the reservoirs are often used for other purposes than electricity production, such as irrigation, drinking water supply and flood protection, the design and operation of reservoirs is a multi-objective management task.

This PhD work aims to contribute to better management of reservoirs in areas with limited water resources, by providing an improved methodology to:

• Assess the real water consumption from hydropower production

• Describe and quantify the increased availability of water due to river regulations

• Guide on future development and operations of reservoirs to minimize water losses

phd thesis department of hydraulic and environmental

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